One of the enduring facts of any tennis era is that injuries end careers. For many, a series of continuous injuries could mean that the player was rushed too early back into play, that there is some structural infirmity, or that the training is not proper.

We have a history of seeing some injuries end careers, largely with knees, and others seemingly ending any sense of rhythm, ending any chance of making an athlete what he or she was.

When we look at child prodigies, some of the more memorable are those who tried the hardest and all seem to have family rather than independent, professional coaches.

Andrea Jaeger won her first professional event at the age of 14 years 28 days in 1977 in Portland. Her career was cut short by a chronic shoulder problem, and she is now a nun.

One article quotes the author of a study that shows cross-training in multiple sports decreases the likelihood of injuries to young tennis players.

Dr. Neeru Jayanthi, lead author of the study, said, "Parents should consider enrolling their children in multiple sports."

"Junior tennis players who play multiple sports at young age are probably less likely to develop injuries because they have a chance to rest from the repetitive overuse of same muscle groups," he said.

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Bidding farewell due to injury yet again.

Among the injuries common to young players noted by Dr. Jayanthi are "muscle strains, ankle sprains, hip injuries, knee cap instability, stress fractures in the spine and tendinitis of the wrist."

While these injuries are likely, muscle tears are also up there on the radar screen. The more severe the injury, the longer to recover.

One would think that with all the effort made by the USTA and other organizations, the problems would diminish. Yet, for all the focus on avoiding injuries, the child prodigy is pushed and often pushes him or herself to succeed.

The push and pull of competition and the parental nature of coaches, many of whom are parents, make this far more likely in tennis than in many other sports. Indeed, no sport other than baseball creates more stress on young muscles and tendons than tennis, with its quick changes of direction and the constant working of the shoulder joints.

So we turn to two of our most famous athletes in the tennis world, both of whom went out at the Australian Open.

Venus Williams and Rafael Nadal are both early Grand Slam winners.

Venus won her first Wimbledon and US Open at 20, and Rafa won his first French Open at 19. Both already had storied careers well before then.

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Yet, as Wikipedia puts it for Williams: "In a career limited by numerous injuries, she is considered to be one of the greatest women's tennis players of all time." So too for Nadal.

There are many sides to both players, and of the two, Nadal surely shines brighter. Yet, both are plagued with injuries far in excess of the normal player.

One can make a lot of excuses for the injuries. Among others, both players train very hard, both use enormous strength to put substantial spin on the ball and both are very quick.

Yet, we are left with the single question, one that will haunt fans of both players. Just how great would these players have been if their careers had been prolonged and injury-free?

We know these things remain a constant in sports.

Records are all that matters. Nothing else does. We can quibble over Pete Sampras never winning the French Open in part because without doing so his record is clearly incomplete. We can argue over the quickest to reach a certain point, fastest to win a certain number of Grand Slams.

The most important of all these points, however, is the record at the end of the career.

It is here that the early signs of injury more often than not create problems for players. And to be truly great, one does not overcome injury. One has to treat injury carefully, change one's game and make the longevity of a career more important than the flash which lasts much shorter and presents so much more problems.

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Of these greats, will Nadal have the shortest career?

Can we blame the families of each of these two magnificent players for what has happened and what is to come? Probably not.

Still, there is the occasional inkling of what might have been by studying those who came before and will come after, whose long careers have included few sidelined events and few tournament-ending injuries during competition.

Look at Roger Federer and almost every great between 1980 and today. While all were largely injury-free (with Bjorn Borg an exception), all obtained their greatness through longevity.

It was something to watch Ken Rosewall play Jimmy Connors, in part because of Rosewall's age, but also because he remained at the top of the tennis world for so long.

Are all child prodigies at greater risk of adult injuries? Almost certainly yes. Is this in part because of the push of family members? Often yes, although the push to make money cannot be discounted given the disproportion of the prosperity of some of the most motivated and successful.

In the end, we cannot believe that injuries will go away from either Williams or Nadal. Williams' career is virtually over and is definitely over if her mother has anything to say about it. While Nadal's career seems on a downward slope, with few seasons that can be played throughout and injury appearing more likely as time goes on.